These are all terms used to describe any item used to assist hearing - e.g. hearing aids, visual alerts, vibrating alarm clocks, vibrating and flashing smoke alarms, pager systems and audio frequency induction loop systems (AFILS).
These are all terms commonly used by the deaf community to refer to audio frequency induction loops (AFILS) - one of the most commonly used assistive devices to improve hearing and communication with the hearing impaired.